The present invention relates to a damping or snubbing arrangement for a railway freight car truck and, more particularly, to a single sloped wedge surface friction shoe for use in a variable damped railway freight car truck snubbing interface between the bolster ends and the sideframe bolster opening.
As set forth in U.S. Pat. Nos. 4,426,934 and 4,637,319, a typical three piece railway freight car truck in service today comprises two laterally spaced sideframes that are typically of an integral cast steel construction, and a bolster extending transversely between such sideframes. The bolster is also typically of an integral cast steel construction. The ends of the bolster are supported on spring groups with the weight of the freight car itself supported on the center plate and side bearings of the bolster top surface. The axle and wheel sets are received in pedestal jaws at each end of the longitudinally aligned sideframes.
As the railway freight car travels down the railroad track, the car is subjected to typical vertical and horizontal component forces that cause the bolster to travel vertically within the sideframe bolster openings. Such motion is absorbed by the spring groups within the sideframe openings. The lower ends of the springs are supported on the spring group support surface of the sideframe with the upper ends of the springs supporting the bottom surface of the bolster ends.
It is necessary to provide snubbing or damping for the bolster so that the motion of the bolster is restricted. Such damping is provided by friction shoes that are located in a so-called friction shoe pockets formed at the outer ends of the bolster. Each end of the bolster includes two such friction shoe pockets formed by sloped surfaces facing laterally on each side of the bolster end. In the variable damped designed railway truck, the bottom of the friction shoe is supported by a spring or spring group that extends to the sideframe spring support surface. This type of truck is known as a variable damped truck because the compression force from the shoe supporting spring varies during relative vertical motion between the bolster and the sideframe. The friction shoes in such variable damped trucks typically have a single sloped wedge surface extending for the entire lateral width of the friction shoe itself.
A vertical wear plate is typically provided along the sideframe vertical face that contacts the vertical wall of the friction shoe.
As discussed in the two patents mentioned above, undesirable wear along a wall of the bolster friction shoe pocket may occur in such trucks as the cast iron friction shoe rubs against the wall during relative movement between the bolster and sideframe. Such wear may eventually create a condition causing the friction shoe to wear in and hang up or lock up thereby restricting the damped motion of the bolster on the spring group. Such lock up causes the tremendous forces associated from the wheels and axles supporting a loaded railway freight car to be transmitted from the sideframes through the friction shoe directly to the sloped surface of the bolster pocket. This condition can lead to excessive stress conditions, the formation of fatigue cracks, and eventual failure of the bolster end structure.
One arrangement to address this problem is set forth in U.S. Pat. No. 4,426,934 and comprises a wear plate positioned within the bolster friction shoe pocket. The purpose of this wear plate would be to protect the sloped surface of the bolster friction shoe pocket as well as the two lateral walls of such pocket. Such arrangement has not been readily accepted and is difficult to install, as such wear plates traditionally become loose in service and can create a condition which may result in further malfunctioning of the railway freight car truck.
Another solution is set forth in U.S. Pat. No. 4,637,319 to mainly address gouging caused by such cast iron friction shoes. Such shoes include a pin hole to allow assembly of the railway freight car truck. It is necessary to hold the friction shoe in the bolster during assembly or servicing of the truck. A support pin is extended through the pin holes in the bolster friction shoe pocket and through the friction shoe itself to allow the friction shoe to be held in position. In service, the pin is removed and the shoe moves vertically in its typical snubbing fashion. However, the shoe wears into the outward bolster pocket wall by the movement of the edges of the pin hole of the friction shoe across the bolster outer pocket. A protrusion tracking the outside of the pin hole edges is formed in the pocket wall to eventually lock up the friction shoe. U.S. Pat. No. 4,637,319 provides solution to this problem by providing a recess along the outer bolster friction shoe pocket to thereby allow the friction shoe movement without wear by the accompanying pin hole in the friction shoe itself.
The present invention provides an improved cast iron or preferably, cast steel friction shoe for use in a snubbing arrangement with a railway freight car truck bolster and sideframe interface.
The friction shoe of the present invention is particularly adapted for use in a variable damped friction snubbing arrangement and railway freight car truck utilizing a variable damped friction shoe arrangement between the bolster end and the sideframe. The friction shoe of the present invention has a unique circular shaped opening on each of the vertical support ribs that will virtually eliminate gouging of the bolster due to edges of the opening wearing into the side walls of the bolster forming the friction shoe pocket. The side walls of the circular opening themselves are tapered.
The reliability of the friction shoe when utilized in a traditional railway freight car truck will also be improved. The friction shoe will not inordinately wear into the cast steel bolster pocket leading to the lock up of the friction shoe and even failure of the bolster itself. Improved safety of railway freight cars utilizing such friction shoes will be readily apparent.
It is a primary object of the present invention to provide an improved friction shoe to provide improved performance in a railway freight car truck.